This invention relates to wood preservation and, more particularly, to wood preservatives based on condensed tannins and the use of same to protect wood against deterioration caused by weathering, fungal attack, etc.
The use of tannin-containing extracts from various woods and bark as wood preservatives is well known. For instance, Lotz et al U.S. Pat. No. 4,732,817 discloses impregnating wood with an aqueous solution containing a tannin extract from a species known to have a desirable resistance to weathering, fungal attack, etc., by itself or in combination with a metal salt, such as cupric chloride or cupric sulfate. In order to prevent leaching of the tannin extract and/or the extract and metallic salt combination, the wood must be subsequently impregnated with a non-ionic surfactant which serves as a fixative material.
The Background of the Invention section of Lotz et al U.S. Pat. No. 4,732,817 describes several other prior techniques for preserving wood with some form of tannin and/or tannic acid. In particular, Mitchell et al U.S. Pat. No. 4,220,688 discloses first impregnating wood with a tannic acid-ethanol solution following by impregnation with an aqueous solution of a metal salt, such as ferric chloride, which complexes with the tannin and the wood. Chow U.S. Pat. No. 4,413,023 discloses wetting the surface of wood with an extract from a decay resistant species of wood. The extract is obtained with acetone, methanol, ethanol or an aqueous alkaline solution such as a borax solution.
Laks. U.S. Pat. No. 4,760,088 discloses the use of chemically modified (i.e., sulfide derivatives) of condensed tannins and copper complexes of such derivatives as wood preservatives.
Applicant has found that the combination of a specific tannin extract, (sulfited tannin extract) which is not effective against fungal attack by itself and a copper (II) salt capable of complexing with such extract is an effective wood preservative.